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Common practice in cars - WHY NOT on boats? | Ask The Expert with NIGEL CALDER
28 February 2026 · 2 min · 3K views
Jan Attenstadt explains boat electronics in studio
What this video covers
Nigel Calder explains why negative-side switching in DC boat circuits violates both ABYC and ISO standards.▶ 0:57 On boats, all negative conductors are typically bonded together and tied to the engine block, lightning protection, and other metal — creating multiple parallel return paths to battery negative.▶ 1:13 If a fault occurs with only a negative-side switch in place, current can bypass the switch through those parallel paths, leaving the circuit live and potentially burning a smaller conductor acting as an unintended return.▶ 1:27 Positive-side switching shuts the entire circuit down cleanly.▶ 1:50 Calder also refutes the automotive argument that switching on the negative side produces zero voltage at the moment of opening: current is identical on both sides of a conductor, so breaking it on the negative side offers no arc-reduction benefit.▶ 2:26 Isolated-ground DC systems require simultaneous switching on both sides, with the switches mechanically linked.▶ 1:54 Adding a negative-side switch at the battery alongside positive-side switching is acceptable, but sole negative-side switching is not.▶ 2:07
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